KR101485381B1 - Wide-angle lens system - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention [0002] The present invention relates to a wide-angle lens system capable of obtaining a wide range of image information in a small size and light weight and high image quality, such as a camera mounted on a camera of a mobile communication terminal, The wide-angle lens system includes: a first glass lens of a meniscus type convex to the object side having a negative refractive power in order from the object side; A second plastic lens of a meniscus type having a negative refracting power and convex to the object side; A third plastic lens of a meniscus type having a positive refractive power and convex to the object side; iris; A fourth plastic lens having a positive refracting power and convex to the object side; .
According to such a configuration, it is possible to reduce the manufacturing cost by limiting the use of the glass lens to one sheet while reducing the number of lenses, and it is possible to provide a wide-angle lens system which realizes a high-resolution wide-

Description

Wide-angle lens system < RTI ID = 0.0 >

BACKGROUND OF THE INVENTION 1. Field of the Invention [0002] The present invention relates to a wide-angle lens system capable of obtaining a wide range of image information in a small size and light weight and high image quality, such as a camera mounted on a camera of a mobile communication terminal,

Generally, a camera is mounted on a mobile communication terminal, a computer, a notebook computer, and a vehicle so that the user can view the surrounding image information or take a picture. In order to reduce the size of a mobile communication terminal and to reduce the size of a computer or a notebook computer, a camera is required to have a small size and a high image quality. In order to prevent a driver from visually disturbing a view, Is required. In addition, such a camera should have a large angle of view to obtain as wide a range of image information as possible.

1 is a view showing a conventional wide-angle lens system.

The wide-angle lens system includes, in order from the object side, a first lens L1, a second lens L2, a third lens L3, a diaphragm AS, a fourth lens L4, a fifth lens L5, A sixth lens L6 is disposed. An optical filter OF such as an infrared ray filter or a cover glass is disposed between the sixth lens 6 and the imaging plane IP.

The first lens L1 and the second lens L2 have a convex meniscus shape on the object side and the radius of curvature of the object side surfaces 1 and 3 is larger than the curvature radius of the upper surfaces 2 and 4 Big.

The third lens L3 and the fourth lens L4 are formed such that the object side faces 5 and 7 are convex toward the object side and the upper faces 6 and 8 are convex upward.

The fifth lens L5 is bonded to the fourth lens L4 to form one lens group. The fifth lens L5 is formed such that the object side surface 9 is concave toward the object side and the upper side 10 is concave upward. The sixth lens L6 is formed so that the object side surface 11 is convex toward the object side and the upper side surface 12 is convex upward.

Such a conventional wide angle lens system is made by mixing 4 to 6 spherical glass lenses and aspheric lenses to realize a wide angle.

In this case, however, the angle of view has been realized to be 170 DEG or less. To realize an angle of view of 185 DEG or more, the total length of the lens (TTL) has been realized to be 11 mm or more.

In such an optical system, in order to realize a wide angle, the size of the product increases, or when the size of the product is small, the angle of view becomes small.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a wide-angle lens system which has a small total lens size, a large angle of view,

According to an aspect of the present invention, there is provided a wide-angle lens system comprising: a first glass lens of a meniscus type convex to the object side, the first glass lens having a negative refractive power in order from the object side; A second plastic lens of a meniscus type having a negative refracting power and convex to the object side; A third plastic lens of a meniscus type having a positive refractive power and convex to the object side; iris; A fourth plastic lens having a positive refracting power and convex to the object side; .

The second plastic lens and the fourth plastic lens are formed of the same material.

The second plastic lens, the third plastic lens, and the fourth plastic lens have aspheric surfaces on both sides.

Further, the refractive power of the first glass lens among the lenses is lowest.

Further, the refractive index of the third plastic lens among the lenses is the highest.

Further, the optical lens system satisfies the following conditions.

0.1 < K1 / Kt < 0.2

Here, K1 is the refractive power of the first glass lens, and Kt is the refractive power of the entire lens system.

Further, the optical lens system satisfies the following conditions.

0.5 < K2 / Kt < 0.65

Here, K2 is the refractive power of the second plastic lens, and Kt is the refractive power of the entire lens system.

Further, the optical lens system satisfies the following conditions.

0.25 < K3 / Kt < 0.55

Here, K3 is the refractive power of the third plastic lens, and Kt is the refractive power of the entire lens system.

Further, the optical lens system satisfies the following conditions.

0.45 < K4 / Kt < 0.6

Here, K4 is the refractive power of the fourth plastic lens, and Kt is the refractive power of the entire lens system.

According to the present invention, it is possible to reduce manufacturing cost by limiting the number of lenses to one and limiting the use of a glass lens, and to provide a wide-angle lens system that realizes a wide-angle high resolution and a small product size.

1 is a view showing a conventional wide-angle lens system.
2 is a diagram showing a configuration of a wide-angle lens system according to an embodiment of the present invention.
3A is a diagram showing a configuration of a wide-angle lens system according to the first embodiment of the present invention.
3B and 3C are graphs of resolution of the wide-angle lens system according to the first embodiment of the present invention.
4A is a diagram showing a configuration of a wide-angle lens system according to a second embodiment of the present invention.
4B and 4C are graphs of resolution of the wide-angle lens system according to the second embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, like reference numerals refer to like elements throughout. The same reference numerals in the drawings denote like elements throughout the drawings.

2 is a diagram showing a configuration of a wide-angle lens system according to an embodiment of the present invention.

The wide-angle lens system includes, in order from the object side, a first glass lens L1, a second plastic lens L2, a third plastic lens L3, a diaphragm 150, and a fourth plastic lens L4.

The first glass lens L1 is a lens closest to the object side. The first glass lens L1 has a negative refracting power and is formed into a convex meniscus type on the object side. The first glass lens L1 is located closest to the external environment, and is formed of a glass material to withstand external scratches, humidity, and converge light of a wide angle. The first glass lens L1 is made of a lens whose both surfaces are spherical, so that the manufacturing cost can be lowered and the assembly can be facilitated. At this time, the curvature radius of the object side surface 111 is larger than the curvature radius of the upper side surface 112. [

It is preferable that the first glass lens L1 is made of a glass lens having an Abbe's number of 50 or more in order to correct chromatic aberration by wavelength. The Abbe number is a number indicating the property of light dispersion of the optical glass. The larger the Abbe number, the less chromatic dispersion occurs and a clear image can be obtained.

It is preferable that the first glass lens L1 has the lowest refractive power among the lenses. Refractive power is 1 / focal length (f), which means the power of the lens. The greater the refracting power, the better the power to break the light. The lowest refractive power is given to the first glass lens (L1) positioned closest to the external environment to minimize the resolution change depending on the temperature.

The second plastic lens L2 is located next to the first glass lens L1. The second plastic lens L2 is a lens of a meniscus type which is convex on the object side and has at least one aspheric surface, and is formed of a plastic material. In the illustrated embodiment, the second plastic lens L2 is formed aspheric on both sides. The second plastic lens L2 may be a commercially available Zeonex F52R.

The second plastic lens L2 is arranged in the same plane as the first glass lens L1 in order to reduce the angle of the light incident on the first glass lens L1 so as to be easily formed on the lens provided after the diaphragm 150. [ It has refracting power. The second plastic lens L2 is preferably made of a lens having an Abbe number of 50 or more. Reference numeral 121 denotes the object side surface of the second plastic lens L2, and 122 denotes the upper surface of the second plastic lens L2.

The third plastic lens L3 is located next to the second plastic lens L2. The third plastic lens L3 is a lens of a meniscus type which is convex on the object side and has at least one aspheric surface, and is made of a plastic material. In the illustrated embodiment, the third plastic lens L3 is formed aspheric on both sides. The third plastic lens L3 has a positive refractive power as opposed to the first glass lens L1 and the second plastic lens L2. Reference numeral 131 denotes the object side surface of the third plastic lens L3, and 132 denotes the upper surface of the third plastic lens L3.

The refractive index of the third plastic lens L3 may be the highest among the lenses. The third plastic lens L3 may have a refractive index of 1.6 or more.

The diaphragm 150 is located next to the third plastic lens L3. Aperture 150 adjusts the size of the aperture to adjust the amount of light passing through the lens.

The fourth plastic lens L4 is located next to the diaphragm 150. The fourth plastic lens L4 has a positive refractive power and is formed of a convex plastic material on the object side. The fourth plastic lens L4 may have a shape in which at least one surface is an aspherical surface and both surfaces are convex. In the illustrated embodiment, the fourth plastic lens L4 is formed aspheric on both sides. It is preferable that the fourth plastic lens L4 is made of a lens having an Abbe number of 50 or more. Reference numeral 141 denotes an object side surface of the fourth plastic lens L4, and 142 denotes an upper surface of the fourth plastic lens L4.

It is preferable that the fourth plastic lens L4 has the highest refractive power among the respective lenses. If a large amount of power is applied to a plastic lens, the focal distance and the like may be changed according to the temperature change, so that a large number of resolution changes depending on the temperature occur. Therefore, among the four lenses, the fourth plastic lens L4).

Zeonex F52R, which is commercially available, may be used as the fourth plastic lens L4. The second plastic lens L2 and the fourth plastic lens L4 are made of the same material, so that the time taken for injection of the lens can be reduced.

An optical filter 160 may be positioned between the fourth plastic lens L4 and the imaging plane 170. [ The optical filter 160 may be an infrared filter, a cover glass, or the like, and the optical filter 160 may be regarded as not affecting the optical performance.

The wide angle lens system of the present invention can reduce the manufacturing cost by using only one glass lens of the first glass lens L1. Since the first glass lens L1 is located at the outermost position in direct contact with the external environment, it is possible to efficiently cope with scratches, humidity and the like by using relatively durable glass.

As can be seen from the following examples, the wide-angle lens system of the present invention is constituted by four lenses in total, limiting the use of the glass lens to one sheet, Resolution image can be realized.

Hereinafter, the first and second embodiments of the wide-angle lens system of the present invention will be described.

1st Example

3A is a diagram showing a configuration of a wide-angle lens system according to the first embodiment of the present invention. 3B and 3C are graphs of resolution of the wide-angle lens system according to the first embodiment of the present invention.

The following shows design data of the wide-angle lens system according to the first embodiment of the present invention.

lens if Radius of curvature thickness Refractive index Abe number Focal length Refractive ability
(| Kn / Kt |) The first lens The first side 12.27641 0.6 1.516798 64.1983 -7.569873 -0.1321 Second side 6.127771 2.266825 The second lens The first side 6.106475 1.051344 1.535 56.0 -1.899609 -0.52642 Second side 3.4 0.577701 Third lens The first side 3.269439 2.463777 1.657 21.4 3.595752 0.278106 Second side 1.179233 0.274641 The fourth lens The first side 1.2 1.241208 1.5.35 56.0 1.767796 0.565676 Second side 1.7605 0.241358

Here, the F number is 2.78, the total focal length is 0.978 mm, the total length (TTL) is 11.12 mm, and the angle of view is 185 deg.

The focal length is the longest in the first glass lens L1 and the shortest in the fourth plastic lens L4. Therefore, the refractive power of the first glass lens L1 is the lowest, and the refractive power of the fourth plastic lens L4 is the highest. The refractivity is the reciprocal of the focal length.

Abbe number is 50 or more for the first glass lens L1, the second plastic lens L2 and the fourth plastic lens L4. Abbe number is the highest in the first glass lens L1 and lowest in the third plastic lens L3.

| Kn / Kt | represents the absolute value of the refractive power of each lens divided by the refractive power of the entire lens, and represents the ratio of the refractive power of each lens to the refractive power of the entire lens.

The refractive power of the first glass lens L1 satisfies the following conditional expression (1).

0.1 < K1 / Kt | < 0.2 [Conditional Expression 1]

Here, K1 is the refractive power of the first glass lens L1, and Kt is the refractive power of the entire lens system.

The refractive power of the second plastic lens L2 satisfies the following conditional expression (2).

0.5 < K2 / Kt | < 0.65 [Conditional expression 2]

Here, K2 is the refraction index of the second plastic lens L2, and Kt is the refraction index of the entire lens system.

The refractive power of the third plastic lens L3 satisfies the following conditional expression (3).

0.25 < K3 / Kt | < 0.55 [Conditional Expression 3]

Here, K3 is the refractive power of the third plastic lens L3, and Kt is the refractive power of the entire lens system.

The refractive power of the fourth plastic lens L4 satisfies the following conditional expression (4).

0.45 < K4 / Kt | < 0.6 [Conditional expression 4]

Here, K4 is the refractive power of the fourth plastic lens L4, and Kt is the refractive power of the entire lens system.

From the above-described conditional expressions 1 to 4, it can be seen that the refractive power of the first glass lens L1 occupies a low ratio in the refractive power of the entire lens system. This is to give a low refractive power to the first glass lens L1 relatively close to the external environment so as to reduce the resolution change according to the temperature change.

The aspherical surface used in this embodiment is obtained from the following equation (1).

[Equation 1]

Where Z: distance from the apex of the lens in the direction of the optical axis,

        Y: distance in the direction perpendicular to the optical axis,

        c: the reciprocal of the radius of curvature (r) at the apex of the lens,

        K: Conic constant,

        A, B, C, D, E, F: aspheric coefficient

In this embodiment, both surfaces of the second plastic lens L2, the third plastic lens L3, and the fourth plastic lens L4 are formed as aspheric surfaces. The conic constant and the aspherical surface coefficient of the second plastic lens L2, the third plastic lens L3 and the fourth plastic lens L4 are as follows.

division The second lens Third lens The fourth lens The first side Second side The first side Second side The first side Second side K 0.000000 -1.129845 -0.227139 0.000000 15.799594 -1.193607 A4 -.2255E-02 0.3345E-01 0.7408E-02 0.1842E + 00 0.1128E + 00 0.5031E-02 A6 -.3603E-03 -.1480E-01 -.1448E-02 0.3113E + 00 -.2874E + 00 0.2768E-01 A8 0.4206E-04 0.1240E-02 0.1669E-02 0.6402E + 00 0.9341E + 00 0.1550E + 00 A10 -.1389E-06 -.1552E-04 -.1715E-05 -.5006E + 01 -.9400E + 00 -1230E + 00 A12 -.5982E-07 0.5205E-04 -.7001E-04 0.9284E + 01 -.1414E + 01 0.9874E-01

3B and 3C show a resolution graph of the wide-angle lens system.

In the graph, the horizontal axis represents the spatial frequency, and the higher the value, the higher the resolution. For example, the highest value 80 on the horizontal axis means that there are 80 pairs of black and white pixels (1 cycle) within 1mm.

The vertical axis represents a modulation transfer function (MTF), which indicates the degree to which a pixel pair can be disassembled. The modulation transfer function is a function of how well the lens system passes the spatial frequency to the image plane. When a certain image (various kinds of spatial frequencies) passes through the lens system, the modulation transfer function value becomes "1" when the image is reproduced at the same brightness, and becomes "0" when the image disappears completely from the image surface.

In the graph, line color, straight line, dotted line, etc. indicate the resolution for each position. In the graph of FIG. 3A, the red solid line indicates the resolution of light entering the center of the lens, the green light is 18.5 ° (half angle), the blue is 35 ° (half angle), and the brown is 57 ° Light and pink represent light coming in at 72 ° (half angle). In the graph of FIG. 3B, red indicates light coming in at 92.5 degrees (half angle).

Referring to FIGS. 3B and 3B, it can be seen that light incident at 72 ° (half angle) has a resolution of 40% even at a resolution of 80 cycles / mm. The outermost light of 92.5 ° (half angle) also has a resolution of 13% at a resolution of 80 cycles / mm.

Therefore, in the wide-angle lens system of this embodiment, it is possible to reduce the manufacturing cost by limiting the use of the glass lens to one sheet while reducing the total number of lenses. In addition, high resolution of a wide angle (185 [deg.]) Can be realized while keeping the overall lens length short.

Second Example

4A is a diagram showing a configuration of a wide-angle lens system according to a second embodiment of the present invention. 4B and 4C are graphs of resolution of the wide-angle lens system according to the second embodiment of the present invention.

The following shows design data of the wide-angle lens system according to the second embodiment of the present invention.

lens if Radius of curvature thickness Refractive index Abe number Focal length Refractive ability
(| Kn / Kt |) The first lens The first side 11.58669 0.58006 1.516798 64.1983 -9.196912 -0.10873 Second side 6.576485 1.957257 The second lens The first side 6.298463 0.728174 1.535 56.0 -1.801810 -0.555 Second side 4.44713 0.558482 Third lens The first side 3.578978 2.342246 1.657 21.4 3.604079 0.277463 Second side 1.311305 0.355609 The fourth lens The first side 1.160121 1.234296 1.535 56.0 1.620846 0.616962 Second side 1.822738 1.369599

Here, the F number is 2.59, the total focal length is 0.9455 mm, the total distance is 10.24 mm, and the angle of view is 185 degrees.

The focal length is the longest in the first glass lens L1 and the shortest in the fourth plastic lens L4. Therefore, the refractive power of the first glass lens L1 is the lowest, and the refractive power of the fourth plastic lens L4 is the highest. The refractivity is the reciprocal of the focal length. Further, the refractive power of each lens satisfies the above-described conditional expressions (1) to (4).

Abbe number is 50 or more for the first glass lens L1, the second plastic lens L2 and the fourth plastic lens L4. Abbe number is the highest in the first glass lens L1 and lowest in the third plastic lens L3.

In this embodiment, both surfaces of the second plastic lens L2, the third plastic lens L3, and the fourth plastic lens L4 are formed as aspheric surfaces. The conic constant and the aspherical surface coefficient of the second plastic lens L2, the third plastic lens L3 and the fourth plastic lens L4 are as follows.

division The second lens Third lens The fourth lens The first side Second side The first side Second side The first side Second side K 0.000000 -1.167239 -0.293257 0.000000 7.471173 -1.138059 A4 -.2487E-02 0.3286E-01 0.5064E-02 0.2585E + 00 0.2294E-01 -.1049E-02 A6 -.4601E-03 -.1868E-01 -.2810E-02 -.2775E + 00 0.1773E + 00 -.1785E-01 A8 0.4906E-04 0.1259E-02 0.1659E-02 0.1774E + 01 -.3501E + 00 0.1654E + 00 A10 -.4258E-06 -.1484E-03 -.7226E-04 -.2800E + 01 0.6518E + 00 -.1465E + 00 A12 -.6260E-07 0.3816E-04 -.6184E-04 0.2531E + 01 -.7858E + 00 0.8730E-01

4B and 4C show a resolution graph of the wide-angle lens system.

In the graph, line color, straight line, dotted line, etc. indicate the resolution for each position. In the graph of FIG. 4A, the red solid line indicates the resolution of the light entering the center of the lens, the green light is 18.5 ° (half angle), the blue is 35 ° (half angle), and the brown is 57 ° Light and pink represent light entering at 73 ° (half angle). In the graph of FIG. 4B, the red color represents light coming in at 92.5 degrees (half angle).

Referring to FIGS. 4B and 4C, it can be seen that light coming in at 72 ° (half angle) has a resolution of 40% even at a resolution of 80 cycles / mm. The outermost light of 92.5 ° (half angle) has a resolution of 40% at a resolution of 80 cycles / mm.

Therefore, in the wide-angle lens system of this embodiment, it is possible to reduce the manufacturing cost by limiting the use of the glass lens to one sheet while reducing the total number of lenses. In addition, high resolution of a wide angle (185 [deg.]) Can be realized while keeping the overall lens length short.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention will be.

111, 121, 131, 141: object side surface
112, 122, 132, 142: upper side
150: aperture
160: Optical filter
170:
L1: 1st glass lens
L2: Second plastic lens
L3: Third plastic lens
L4: fourth plastic lens

Claims (9)

In a wide-angle lens system,
A first glass lens of a meniscus type convex on the object side and having a negative refracting power in order from the object side;
A second plastic lens of a meniscus type having a negative refracting power and convex to the object side;
A third plastic lens of a meniscus type having a positive refractive power and convex to the object side;
iris;
A fourth plastic lens having a positive refracting power and convex to the object side;
Lt; / RTI &gt;
A wide-angle lens system satisfying the following conditions.
0.5 < K2 / Kt &lt; 0.65
Here, K2 is the refractive power of the second plastic lens, and Kt is the refractive power of the entire lens system. In a wide-angle lens system,
A first glass lens of a meniscus type convex on the object side and having a negative refracting power in order from the object side;
A second plastic lens of a meniscus type having a negative refracting power and convex to the object side;
A third plastic lens of a meniscus type having a positive refractive power and convex to the object side;
iris;
A fourth plastic lens having a positive refracting power and convex to the object side;
Lt; / RTI &gt;
A wide-angle lens system satisfying the following conditions.
0.25 < K3 / Kt &lt; 0.55
Here, K3 is the refractive power of the third plastic lens, and Kt is the refractive power of the entire lens system. 3. The method according to claim 1 or 2,
Wherein the second plastic lens, the third plastic lens, and the fourth plastic lens are aspheric on both sides. 3. The method according to claim 1 or 2,
And the refractive power of the first glass lens is the lowest among the lenses. 3. The method according to claim 1 or 2,
Wherein the third plastic lens has the highest refractive index among the lenses. 3. The method according to claim 1 or 2,
A wide-angle lens system satisfying the following conditions.
0.1 < K1 / Kt < 0.2
Here, K1 is the refractive power of the first glass lens, and Kt is the refractive power of the entire lens system. 3. The method according to claim 1 or 2,
Wherein the second plastic lens and the fourth plastic lens are made of the same material. delete 3. The method according to claim 1 or 2,
A wide-angle lens system satisfying the following conditions.
0.45 < K4 / Kt < 0.6
Here, K4 is the refractive power of the fourth plastic lens, and Kt is the refractive power of the entire lens system.

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